This invention relates in general to cleaning lubricants from steel strip and, more particularly, to the electrolytic removal of lubricants from steel strip by the application of a high-current-density in an alkaline electrolyte.
U.S. Pat. No. 3,668,050, incorporated herein by reference, teaches an alkaline cleaning process using high current densities wherein particularly good cleaning is achieved at current densities of from 4,320 to 8,640 amps per square foot. The process shown therein is primarily limited to the cleaning of wire. With respect to sheet and strip having significantly greater surface area, the utilization of current densities in excess of 4,000 amps per square foot requires inordinately high power. Additionally, current densities of this order require very significant stirring of the electrolyte to overcome concentration polarization effects. The stirring methods shown by the above patent are generally ineffective for electrolyzing sheet or strip with large planar surfaces. However, stirring methods which are more applicable to strip are known in the art.
U.S. Pat. Nos. 3,471,375 and 3,535,222, incorporated herein by reference, show the use of high-current-density electrochemical apparatus and processes for pickling and anodizing aluminum strip.
U.S. Pat. No. 3,650,935, incorporated herein by reference, teaches a method and apparatus for high-current-density pickling of metal objects. This patent teaches the desirability of counter-current flow of electrolyte in combination with an electrode gap which decreases in the direction of movement of the metal being pickled for the purpose of achieving maximum electrochemical efficiency. The patent teaches that this tapered electrode spacing leads to the current densities required in conventional methods with a lower power input.
However, we discovered when trying to adapt the state-of-the-art technology to high speed cleaning of steel strip that unduly high power requirements were needed. In addition, cleaning was not satisfactory.